Ball mill for forming liquid suspensions of finely divided solid material



Jan. 31, 1967 A. E. ZISELBERGER 3,301,495

BALL MILL FOR FORMING LIQUID SUSPENSIONS OF FINELY DIVIDED SOLID MATERIAL Original Filed May 22, 196-3 IN VEN TOR. ALBERT E. ZISELBERGER ATTORNEYS United States Patent 3,301,495 BALL MILL FOR FQRMHNG LIQUID SUSPENSIONS OF FINELY DIVIDED SiOLID MATERIAL Albert E. Ziselberger, Cody, 'Wyo., assignor of one-third part of anundivided sixty-four percent each to Sid H. Eliason, Edward L. Hildebrand, Sid H. Eliason, 11a, all of Salt Lake City. Utah, and eight percent of the entire right to W. C. Headlee, Cody, Wyo. Original application May 22, 1963, Ser. No. 282,485. Divided and this application Mar. 26, 1965, Ser. No. 459365 3 Claims. (Cl. 241--62) This is a division of U.S. application Serial No. 282,485, filed May 22, 1963.

This invention relates to the manufacture of gypsum wallboard products and is particularly concerned with the control of set of the gypsum stucco slurry as deposited on and as covered by continuous strip sheets of heavypaper prior to cutting the resulting continuous strip of final board into relatively short pieces for marketing.

In the art concerned, it is traditional practice to accelerate set of the deposited gypsum stucco slurry by adding, to the calcined gypsum mix used in making up the slurry, a dry powder derived by grinding previously manufactured gypsum blocks. It has long been known that the powder thus obtained has a crystal structure and perhaps other physical and chemical characteristics which peculiarly adapt it to serve as a set accelerator.

Although thought has been given heretofore, by many concerned with this art, to the possibility of utilizing other gypsum materials in both dry and wet form as a set accelerator, thereby to avoid the necessity of first manufacturing and grinding gypsum blocks for the purpose, no successful'method of doing this has been heretofore evolved.

It is well recognized that, in many instances of the manufacture of gypsum wallboard products, it would be highly advantageous to avoid the necessity of importing or of specially manufacturing gypsum blocks for the purpose of providing the required set accelerator.

Accordingly, a principal objectin the making of the present invention was to enable ordinary calcined gypsum to be used as a set accelerator for gypsum stucco slurry.

In the accomplishment of this object, I found it necessary to prepare a thin, aqueous suspension of calcined gypsum fines, having about the consistency of water,'and to maintain these fines in suspension for a limited time. From the indications to date, it appears that the duration of such time has a definite bearing on the degree of acceleration of set and, along with the quantity of suspended fines going into the mix, determines by how much time the set of the stucco slurry is accelerated over what would prevail without the addition of an accelerator to the mix.

The aqueous suspension of calcined gypsum fines serving as the set accelerator is produced and maintained for the requisite time period prior to use by means of pulverizing agitation advantageously achieved by utilizing a pulverizing mill, preferably a ball mill of appropriate length with provision for continuous feed of both dry calcined gypsum fines and water and with continuous discharge of the final aqueous suspension.

There are various types of mills that can be used for the purpose, but part of the invention is concerned with a special ball mill that I have developed in order to insure continuous satisfactory operation and results over extended production periods without danger of plugging or down-time for cleaning.

Specific procedures and apparatus presently regarded as the best mode of carrying out the invention in actual commercial practice are described hereinafter with reference to the accompanying drawing. From these, other more specific objects and features of the invention will become apparent.

ice

In the drawing:

FIG. 1 represents an elevational view of that portion of a plant for producing gypsum wallboard products that is concerned with the invention; and

FIG. 2, a transverse vertical section taken on the line 2-2 of FIG. 1 through the special ball mill developed for the purpose of carrying out the process of the invention to best advantage.

Referring to the drawing:

The illustrated plant includes a usual mixer 10 for mixing calcined gypsum and water to produce a gypsum stucco slurry which is continuously deposited in usual manner on a web or strip of heavy paper (not shown) and is spread and smoothed thereon by standard equipment (not shown) prior to the application of a corresponding cover web or strip of heavy paper (not shown) to yield a continuous web or strip of plaster board, lath, or similar product which is carried by an endless belt (not shown) until in condition for cutting into relatively short lengths.

As previously indicated, the invention is concerned with the addition to the gypsum stucco slurry of a set accelerator, so that the slurry sandwiched between the heavy paper webs or strips will harden sooner than it would otherwise and will permit early cutting of the continuous web or strip of board into individual product form, thereby avoiding an uneconomic length for the boardcarrying belt and the plant building or undesirable slowdown in belt speed and consequent reduced output for the plant.

In the form illustrated, the set accelerator is prepared by continuously feeding finely-divided, dry, calcined gypsum from any suitable source into one end of a special, elongate ball mill 11. This is advantageously accomplished by utilizing a standard type of dry chemical feeder 12, which is constructed to feed material at a given measured rate by weight. Such feeder is arranged to discharge directly into a flushing type of hopper 13, wherein water is supplied by a pipe 14 at a given measured rate by volume to a hollow rim 13a and from there directly into the interior of the hopper by way of a series of jet discharge orifices 15 directed to produce a swirling action within the hopper which will effectively pick up the particles of dry gypsum and aid in placing them in suspension as they are fed into one end of the ball mill.

'The ball mill 11 comprises an elongate, stationary drum 16 and a deeplp fluted, columnar rotor 17, FIG. 2, extending the entire length thereof, with stub shafts 18 and 19, FIG. 1, at opposite ends passing through packing glands 20a and 21a in the closed ends 20 and 21, respectively, of the drum and being journaled in and supported by bearing stands 22 and 23, respectively. Legs 24 firmly support drum 16.

There are only small clearances between the respective flute spines 17a of rotor 17 and the inner wall of drum 16, e.g., one-sixteenth of an inch each, and the flute valleys 17b lying between adjacent spines are packed with grinding balls 25 sufliciently loosely that the rotor can be easily turned.

For a production schedule of 360 pounds of gypsum stucco per minute with a board-carrying belt speed of feet per minute, I have found that a feed of one pound of dry calcined gypsum to four gallons of water per minute and a milling time of four minutes for the set accelerator aqueous suspension will produce a satisfactory set in five minutes as against thirty minutes without such set accelerator. This setting time can be shortened or lengthened by increasing or decreasing, respectively, the quantity of calcined gypsum used with respect to the water, or, vice versa, and, to a certain extent, by increasing or decreasing, respectively, the milling time.

ing proportion of the feed materials.

The temperature of the water used should be about 85 F.

For the above production schedule in the specific instance illustrated, the length of the drum 16 of the ball mill is eight feet, the inside diameter is ten inches, the diameter of the rotor from spine tip to spine tip is nine and seven-eighths inches and from valley bottom to valley bottom is five inches, and grinding ball diameter is three quarters of an inch.

The rotor 17 is turnedby any suitable prime mover,

preferably an electric motor (not shown) connected by a sprocket drive 26 to one of thestub shafts. In the specific instance, a rotation rate for the rotor of about sixty r.p.m. is very satisfactory.

The aqueous suspension of calcined gypsum fines utilized as a set accelerator is continuously discharged from the opposite end of ball mill 11 and is passed into the mixer 10, where it becomes part of the gypsum stucco slurry used in the production of gypsum board products. For this purpose, a discharge orifice 27 is provided through the cylindrical wall of drum 16 at the uppermost portion of its circumferential periphery and at the end opposite that at which feed spout 13b of charging hopper 13 opens into the drum. A trough 28 receives the discharging material and passes it directly into mixer by way of a conduit 29. In thespecific instance, feed spout 13b of hopper 13 has an inside diameter of two inches and discharge orifice 27 of the drum 16 is a slot one and one-half inches long and one-half inch wide.

Although calcined gypsum fines from any source can be used as the feed material for'the pulverizing mill, I prefer to use reject fines from a scalper screen operating on calcined gypsum discharged from a cyclone classifier following calcination of raw gypsum rock. This material is of such size that 90 to 97 percent of it will pass through a 100 mesh screen. It is normally regarded as a Waste material, but is ideal for the present purpose. It is well known in the art that potassium sulfate and certain other materials also serve as set accelerators. either alone as a dry powder or mixedavith finely ground gypsum block material. I have found that these materials can also be used in aqueous suspension in accordance with the present invention.

Although I have found a ratio of four gallons of water to one pound ofaccelerator fines to be ideal for preparing the aqueous suspension in the specific instance herein described, that should not be regarded as a limitdicated, the extent of acceleration desired is an important factor. In general, the ratio of water to calcined gypsum fines will range between one to one and six to one, depending upon the setting action. Structural specifications for the ball mill will also vary in accordance with board-carrying belt speed. Increased volume per minute canbe obtained by increasing drum and rotor diameters and increased time of maintaining the suspension by increasing their lengths. In all instances, however, the aqueous suspension of the invention is a free-flowing, watery liquid.

Whereas there are specifically described and illustrated As previously in- 4 preferr'edprocedure and construction presently regarded as the best mode of carrying out the invention, it should be understood that various changes can be made and other procedures and constructions adopted without departing from the inventive subject matter particularly pointed out and claimed herebelow.

I claim: 1. A balLmill-for forming liquid suspensions of finely divided solid mineral particles, comprising an elongate, stationary, substantially horizontal drum; a deeply fluted, columnar rotor extending along the length of the interiorof said drum, axially thereof, with the termini of the flute spines also extending along the length of the interior of said drum and being closely spaced from. the inner wall of said drum; masses of grinding balls packed within the respective flute valleys and confined therein and carried along therewith by respective pairs of mutually adjacent flute spines which define said valleys, so as to bear and roll against the inner wall of said drum as said rotor rotates, the spacing between the respective termini of the spines and the inner wall of the drum being considerably less than the respective diameters of said balls, so the balls in each fiute valley will be retained therein and so that there is an elongate opening restricted to narrow slit character defined between each flute terminus and the inner wall of the drum solely as clearance for rotor rotation, each flute valley being otherwise closed along its length; means at one end of the drum for flowing the initial suspension of material into the ball mill; means at the other end of the drum for flowing the final suspension of material from the ball mill; and means for rotating the rotor.

2. A ball mill in accordance with claim 1, including means associated with the initial-suspension-fiowing means for forming a liquid suspension of finey divided,

solid, mineral particles as a liquid, and such particles in dry form are fedto the mill.

3. A ball mill in accordance with claim 2, whereinthe means for flowing the final suspension from the billis an opening through the top of the drum at the. discharge end thereof.

' References Qited by the Examiner UNITED STATES PATENTS 2,014,640 9/1935 Wales 241-172 XR 2,041,287 5/1936 Frisch 241172 XR 2,754,067 7/1956 Klugh 241-171 XR 2,824,701 2/1958 Vester 24121 2,993,656 7/1961 Ratkowski 241- XR FOREIGN PATENTS 24, 127 2/ 1919 Denmark. 402,660 9/1909 France. 371,793 3/1932 Great Britain.

WILLIAM W. DYER, JR., Primary Examiner.

ROBERT C. RIORDON, H. F. PEPPER,

Assistant Examiners. 

1. A BALL MILL FOR FORMING LIQUID SUSPENSIONS OF FINELY DIVIDED SOLID MINERAL PARTICLES, COMPRISING AN ELONGATE, STATIONARY, SUBSTANTIALLY HORIZONTAL DRUM; A DEEPLY FLUTED, COLUMNAR ROTOR EXTENDING ALONG THE LENGTH OF THE INTERIOR OF SAID DRUM, AXIALLY THEREOF, WITH THE TERMINI OF THE FLUTE SPINES ALSO EXTENDING ALONG THE LENGTH OF THE INTERIOR OF SAID DRUM AND BEING CLOSELY SPACED FROM THE INNER WALL OF SAID DRUM; MASSES OF GRINDING BALLS PACKED WITHIN THE RESPECTIVE FLUTE VALLEYS AND CONFINED THEREIN AND CARRIED ALONG THEREWITH BY RESPECTIVE PAIRS OF MUTUALLY ADJACENT FLUTE SPINES WHICH DEFINE SAID VALLEYS, SO AS TO BEAR AND ROLL AGAINST THE INNER WALL OF SAID DRUM AS SAID ROTOR ROTATES, THE SPACING BETWEEN THE RESPECTIVE TERMINI OF THE SPINES AND THE INNER WALL OF THE DRUM BEING CONSIDERABLY LESS THAN THE RESPECTIVE DIAMETERS OF SAID BALLS, SO THE BALLS IN EACH FLUTE VALLEY WILL BE RETAINED THEREIN AND SO THAT THERE IS AN ELONGATE OPENING RESTRICTED TO NARROW SLIT CHARACTER DEFINED BETWEEN EACH FLUTE TERMINUS AND THE INNER WALL OF THE DRUM SOLELY AS CLEARANCE FOR ROTOR ROTATION, EACH FLUTE VALLEY BEING OTHERWISE CLOSED ALONG ITS LENGTH; MEANS AT ONE END OF THE DRUM FOR FLOWING THE INITIAL SUSPENSION OF MATERIAL INTO THE BALL MILL; MEANS AT THE OTHER END OF THE DRUM FOR FLOWING THE FINAL SUSPENSION OF MATERIAL FROM THE BALL MILL; AND MEANS FOR ROTATING THE ROTOR. 